Try typing the word in, then hit the 'preview' button. If it is picked up by the obscenity filter, [oops!] and an alternative word will pop up.
That's not to say that if it isn't picked up initially that it won't be added - my mind is angelically clean so I had to revert to a potty-mouthed friend to identify some more obscure vulgarities.
Occasionally, it will correct words like Ant mentioned that can be used inappropriately but sometimes just have absolutely valid and non-offensive uses, too. Try typing in the name of another very large Q&A site, too. But my grandma would still think that using some colloquialisms to describe faeces is inappropriate, and certainly not to be done in front of children, so that's the level of appropriateness that we apply. Call it the 'Vera' test, if you like. (And if you use bad language, expect her at your front door with a bar of carbolic soap to wash your mouth out.)